1. Field of the Invention
This invention relates to a switching matrix in a network of a telephone switching system. More particularly, this invention relates to an improvement on a switching matrix equipment with relay coils at crosspoints in which designation of a desired crosspoint in the switching matrix selectively energizes the relay coil of a relay related to the designated crosspoint to close a speech path of the switching network through the closed contacts of the relay.
2. Description of the Prior Art
In a switching network of a telephone switching system, a desired speech path in the network is formed by closing the contacts of the relay associated with the speech path. Generally, such a switching network uses a matrix with a number of crosspoints each comprising a relay coil for closing the related relay contacts. Specifying a proper row and a proper column selects and energizes the relay coil correspondingly associated with a desired speech path. In the switching matrix using relays at the crosspoints, the desired relay having been selected and energized is held with a small current restricted by a resistor used or the like, with a view of the reduction of power consumption produced by the current flowing through the relay coil. In this case, since it is necessary to make the current flow only through the relay coil selected, a relay contact, which is closed by energization of the relay coil related is used in series with the coil, for the purpose of setting up an electrical path permitting the holding current to flow therethrough. The switching matrix with such a construction, however, is disadvantageous in some points. For example, at the moment that the contact connected in series with the relay coil, which is one of the contacts of the selected and energized relay, is closed, a holding power source for holding the relay is applied to the contact, in addition to a drive power source for driving the relay. Thus, an excessive current flows through the contact, leading to wear of the contact. In the case of the reed relay using a reed switch, welding between the reed tips becomes problematic. The reed relay case suffers from another disadvantage that such a contact as to hold the relay is necessary in addition to the contact to close the speech path and thus when an expensive reed switch is used, the switching matrix using such is costly.
In case where switching matrices arranged in multistage connection, when crosspoint switches at the respective stages are held in their operations, it is necessary to successively select and hold the relay coils at the stages correspondingly related to the crosspoint switches. In a system of the type in which the relay coil is held through the associated relay contact, the succeeding relay coil cannot be driven until the preceding relay contact is closed. Therefore, a relatively long time must be taken until all the relay coils are selected and held.
There has been used another example to selectively hold the relay coils, in which three-terminal diodes are used in place of the relay contacts. This example is free from the problems of the relay contact wear or the reed tip welding. The example, however, needs lead wires for gate current supply to the gate terminal of the diode. Accordingly, a power source to supply the gate current is required and superfluous and troublesome work is necessary for connecting the lead wires to the gate terminal of the diode. A general switching equipment employs a multistage connection of switching matrices. Such a switching equipment of the gate control type rejects the multistage connection of the relays to close the crosspoint switches in those matrices so that selection, holding and release of a desired relay must be made for each stage.